A radiological image processing apparatus accumulates radiation energy transmitted through an object under examination, in an image sensor called “flat panel radiation detector (FPD: Flat Panel Detector)”, and converts it into electric signals for visualization. At this time, the FPD accumulates linear radiation energy transmitted through the object, but at the same time accumulates also low-energy radiation scattered about when transmitted through the object. Consequently, image quality will be lowered, such that the contrast of the radiological image taken is lowered by the scattered radiation. Usually, in order to remove this scattered radiation, radiography is carried out through a grid constructed by arranging alternately a radiation absorbing layer which uses lead or the like with a high rate of radiation absorption and a radioparent layer which uses aluminum, paper or the like with a low rate of radiation absorption.
However, when an object is radiographed through the grid, a figure with a striped pattern (grid figure) under the influence of the radiation absorbing layers will be superimposed on a radiological image which is a photo image. Conventionally, to reduce this grid figure, there is an oscillating system for oscillating the grid during radiography. However, the apparatus is enlarged by realizing this oscillating system, to give rise to a problem of high cost, for example.
Then, in order to remove the grid figure with variations due to the grid, there is a technique in which, based on sensitivity variations of a plurality of pixels constituting an image sensor, an image for correction for correcting a radiological image of an object under examination is created from image data obtained beforehand through the grid and without the object, and image components due to the grid are removed using the image for correction (see Patent Document 1, for example). In addition, there are techniques of carrying out filtering based on a relationship between grid frequency relating to grids and sampling frequency of image sensors, in order to cope with two or more types of grids and various image sensors (see Patent Documents 2-4, for example).
[Patent Document 1]
Unexamined Patent Publication No. 2005-324069
[Patent Document 2]
U.S. Pat. No. 2,507,659 (pages 1, 3-5, and FIGS. 1-3, 7)
[Patent Document 3]
Unexamined Patent Publication No. 2004-344670 (page 7, FIG. 7, Table 1)
[Patent Document 4]
Unexamined Patent Publication No. 2003-260053 (page 6, Table 1)